RESUMEN
BACKGROUND: We describe two patients with factor IX deficiency and high levels of inhibitors to factor IX who developed anaphylaxis to factor IX. OBJECTIVE: The aim of this study was to develop a skin test, RAST, and desensitization protocol for factor IX allergy. METHODS: The patients were evaluated by skin test and RAST to factor IX. They also underwent desensitization to factor IX. RESULTS: Both patients had positive skin test and RAST reactions to factor IX. Control subjects had negative reactions. Both patients were successfully desensitized to factor IX by using two different desensitization protocols. The patients' skin test and RAST reactions to factor IX converted to negative after desensitization. CONCLUSIONS: IgE-mediated reactions to factor IX do occur and may be diagnosed with the use of skin test and RAST. Patients with this type of reaction may be successfully desensitized to factor IX.